Well it matters some, but yes in my experience, this is what most people only concern themselves with. Hosting companies know what sells and what confuses people. People can easily understand what *unlimited* disk space and bandwidth means, but will be confused when you try to start explaining to them the server's CPU allocation. They want customers and a confused mind always says no.
To answer your question though, if you truly do have unlimited on those things, that means you theoretically upload any amount of videos on your site you want (disk space).
You could also have your videos streamed and viewed an unlimited amount of times (bandwidth).
Problem could be...
Bandwidth and CPU usage are close relatives. CPU usage comes into effect when your website has to work extra hard because of your traffic (or something your site is doing) which causes lots of CPU usage, usually all at one time.
Imagine trying to run 12 different programs on your home at the same time. What might happen?
Your computer might lock up or everything will run REALLY slow.
Your site is hosted on a computer with lots of other websites. You don't own 100% of the CPU, John Doe next to you needs some too. So your site can only use so much at one time and then it must wait.
Make sense? Or do I need more coffee? :)